A ballistic vest, bulletproof vest or bullet-resistant vest is an item of personal armor that helps absorb the impact from firearm-fired projectiles and shrapnel from explosions, and is worn on the torso. Soft vests are made from many layers of woven or laminated fibers and can be capable of protecting the wearer from small-caliber handgun and shotgun projectiles, and small fragments from explosives such as hand grenades.

Metal or ceramic plates can be used with a soft vest, providing additional protection from rifle rounds, and metallic components or tightly-woven fiber layers can give soft armor resistance to stab and slash attacks from knives and similar close-quarter weapons. Soft vests are commonly worn by police forces, private citizens, security guards, and bodyguards, whereas hard-plate reinforced vests are mainly worn by combat soldiers, police tactical units, and hostage rescue teams.

Modern body armor may combine a ballistic vest with other items of protective clothing, such as a combat helmet. Vests intended for police and military use may also include ballistic shoulder and side protection armor components, and bomb disposal officers wear heavy armor and helmets with face visors and spine protection.

Overview

Ballistic vests use layers of very strong fiber to "catch" and deform a bullet, mushrooming it into a dish shape, and spreading its force over a larger portion of the vest fiber. The vest absorbs the energy from the deforming bullet, bringing it to a stop before it can completely penetrate the textile matrix. Some layers may be penetrated but as the bullet deforms, the energy is absorbed by a larger and larger fiber area.

While a vest can prevent bullet penetration, the vest and wearer still absorb the bullet's energy. Even without penetration, modern pistol bullets contain enough energy to cause blunt force trauma under the impact point. Vest specifications will typically include both penetration resistance requirements and limits on the amount of impact energy that is delivered to the body.

Vests designed for bullets offer little protection against blows from sharp implements, such as knives, arrows or ice picks, or from bullets manufactured of non-deformable materials, i.e., those containing a steel core instead of lead. This is because the impact force of these objects stays concentrated in a relatively small area, allowing them to puncture the fiber layers of most bullet-resistant fabrics.

Textile vests may be augmented with metal (steel or titanium), ceramic or polyethylene plates that provide extra protection to vital areas. These hard armor plates have proven effective against all handgun bullets and a range of rifles. These upgraded ballistic vests have become standard in military use, as soft body armor vests are ineffective against military rifle rounds. Corrections officers and other law enforcement officers often wear vests which are designed specifically against bladed weapons and sharp objects. These vests may incorporate coated and laminated para-aramid textiles or metallic components.

Progress in fiber science

In recent years advances in material science have opened the door to the old idea of a literal "bulletproof vest" that will be able to stop handgun and rifle bullets with a soft textile vest without the assistance of heavy and cumbersome extra metal or ceramic plating. In fact the progress in fibers materials is quite slow by comparison to the rate of change in some other technical disciplines. The most recent offering from Kevlar called Protera was released in 1996. Current soft body armor can stop most handgun rounds which has been the case for perhaps 15 years. However armor plates are needed to stop rifle rounds and steel core handgun rounds such as 7.62x25. The para-aramids have not progressed beyond the limit of 23 grams per denier in fiber tenacity.

Modest ballistic performance improvements have been made by new producers of this fiber type. Much the same can be said for the UHMWPE material; the basic fiber properties have only advanced to the 30–35 g/d range. Improvements in this material have been seen in the development in cross-plied non-woven laminate eg Spectra Shield. The major ballistic performance advance of fiber PBO is perhaps a classic cautionary tale in materials science. This fiber permitted the design of handgun soft armor that was 30–50% lower in mass as compared to the aramid and UHMWPE materials. However this higher tenacity was delivered with a well-publicized weakness in environmental durability.

Akzo-Magellan (now DuPont) teams have been working on fiber called M5 fiber, however its announced startup of its pilot plant has been delayed more than 2 years. Data suggests if the M5 material can be brought to market, its performance will be roughly equivalent to PBO. In May 2008, the Teijin Aramid group announced a “super-fibers” development program. The Teijin emphasis appears to be on computational chemistry to define a solution to high tenacity without environmental weakness.

The materials science of second generation “super” fibers is complex, requires large investments, and represent significant technical challenges. Research aims to develop artificial spider silk which could be super strong, yet light and flexible. Other research has been done to harness nanotechnology to help create super-strong fibers that could be used in future bulletproof vests.

Textile wovens and laminates research

Finer yarns and lighter woven fabrics have been a key factor in improved ballistic results. The cost of ballistic fiber goes up dramatically as yarn size goes down, so it is unclear how long this trend can continue. The current practical limit of fiber size is 200 denier with most wovens limited at the 400 denier level. Three-dimensional weaving with fibers connecting flat wovens together into a 3D system are being considered for both hard and soft ballistics. Team Engineering Inc is designing and weaving these multi layer materials. Dyneema DSM has developed higher performance laminates using a new, higher strength fiber designated SB61, and HB51. DSM feels this advanced material provides some improved performance, however the SB61 “soft ballistic” version has been recalled. At the Shot Show in 2008, a unique composite of interlocking steel plates and soft UHWMPE plate was exhibited by TurtleSkin. In combination with more traditional woven fabrics and laminates a number of research efforts are working with ballistic felts. Tex Tech has been working on these materials. Like the 3D weaving, Tex Tech sees the advantage in the 3-axis fiber orientation .

Developments in ceramic armor

Ceramic materials, materials processing and progress in ceramic penetration mechanics are significant areas of academic and industrial activity. This combined field of ceramics armor research is broad and is perhaps summarized best by The American Ceramics Society. ACerS has run an annual armor conference for a number of years and complied a proceedings 2004–2007. An area of special activity pertaining to vests is the emerging use of small ceramic components. Large torso sized ceramic plates are complex to manufacture and are subject to cracking in use. Monolithic plates also have limited multi hit capacity as a result of their large impact fracture zone These are the motivations for new types of armor plate. These new designs use 2 and 3 dimensional arrays of ceramic elements that can be rigid, flexible or semi-flexible. Dragon Skin body armor is one these systems. European developments in spherical and hexagonal arrays have resulted in products that have some flex and multi hit performance. The manufacture of array type systems with flex, consistent ballistic performance at edges of ceramic elements is an active area of research. In addition advanced ceramic processing techniques arrays require adhesive assembly methods. One novel approach is use of hook and loop fasteners to assemble the ceramic arrays .

Nanomaterials in ballistics

Currently, there are a number of methods by which nanomaterials are being implemented into body armor production. The first, developed at University of Delaware is based on nanoparticles within the suit that become rigid enough to protect the wearer as soon as a kinetic energy threshold is surpassed. These coatings have been described as shear thickening fluids. These nano-infused fabrics have been licensed by BAE systems however as of mid 2008, no products have been released based on this technology.

In 2005 an Israeli company, ApNano, developed a material that was always rigid. It was announced that this nanocomposite based on tungsten disulfide nanotubes was able to withstand shocks generated by a steel projectile traveling at velocities of up to 1.5 km/s. The material was also reportedly able to withstand shock pressures generated by the impacts of up to 250 metric tons-force per square centimeter (24.5 gigapascals; 3,550,000 psi). During the tests, the material proved to be so strong that after the impact the samples remained essentially unmarred. Additionally, a recent study in France tested the material under isostatic pressure and found it to be stable up to at least 350 tf/cm² (34 GPa; 5,000,000 psi).

As of mid-2008, spider silk bulletproof vests and nano-based armors are being developed for potential market release. Both the British and American militaries have expressed interest in a carbon fiber woven from carbon nanotubes that was developed at University of Cambridge and has the potential to be used as body armor. In 2008, large format carbon nanotube sheets began being produced at Nanocomp.

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